With the rapid market expansion in the fields of notebook personal computers and cellular phones, among others, the demand for small-sized, high-energy-density and high-capacity secondary batteries for use in such machines or instruments has been growing. To meet such demand, secondary batteries in which the electrochemical reaction involving the charge transfer with alkali metal ions, such as lithium ions, serving as charge carriers is utilized have been developed. In particular, lithium ion secondary batteries are utilized as high-capacity secondary batteries high in energy density and excellent in stability in various electronic machines and instruments. In such lithium ion secondary batteries, a lithium-containing transition metal oxide is generally used as an active material in the positive electrode, and carbon as an active material in the negative electrode, and charging and discharging are carried out utilizing the insertion and elimination reactions of lithium ions into and from these active materials.
In recent years, secondary batteries in which radical compounds are utilized as electrode active materials directly contributing to the electrode reaction have been proposed for further capacity increases (cf. Patent Document 1).
In the above-mentioned secondary batteries, organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxofuran, sulfolane, dimethylformamide, dimethylacetamide and N-methyl-2-pyrrolidone are used, either singly or in the form of a mixture of two or more, as solvents for constituting electrolytic solutions transporting charge carriers between the negative and positive electrodes.
However, the radical compounds so far proposed are unsatisfactory in solvent stability and the electrode active material is eluted into the solvents for constituting electrolytic solutions and, therefore, there arises a problem that the stability of the secondary battery performance becomes unsatisfactory.    Patent Document 1: Japanese Kokai Publication 2002-151084